8/19/2019 Dynamic Model of IGBT

1/1

282

A.

HADDI

et al.

The

SPICE

parameters

which

provide

for

adjustment

of

saturation

current,

conductivity,

and

static

saturation

voltage

of

the

IGBT

are:

Kp

 Transconductance

coefficient ,

  and

L

 channel

width

and

length

respectively ,

G MM

bulk

threshold

parameter),

PHI

 surface

potential),

and

L M D

channel-length

modulation)

for

the

MOSFET

element,

and

the

current

gain

for the

BJT.

II.2.

Dynamic

Model

of IGBT

After

calibration

of the

static

parameters,

one can

proceed

with the

dynamic

model.

Two

branches,

with

components

names

indicated

GD

and

DG

in the

sub-circuit,

between

the

gate

and drain of

the

MOSFET

are

used

to

simulate

the

dynamic parameters

[9].

Typical

dynamic

parameters,

used to characterize the

IGBT,

are the

switching

characteristics

times:

rise time

 tr ,

fall

time

 tf ,

turn-on

delay

time

 tdon ,

turn-off

delay

time

 tdoer ,

turn-on

time

 ton ,

and turn-off time

 tor ,

with:

ton

tr

+tdon

and

torf

tf-+-

tdoff.

Fall

Time

Calibration

The

biggest

limitation

to

the turn-off

speed

of

an

IGBT is

the lifetime

of

the

minority

carriers in the

n-

epi. layer, i.e.,

the base

of

the

p-n-p

bipolar

transistor.

The

charges

stored

in

the

base

produce

a

characteristic

 tail in

the current

waveform

of an

IGBT

at

turn-off.

When

the

MOSFET s

channel

turns

off,

electron

current decreases

and the

IGBT

current

drops

rapidly

to

the level

of

the

hole recombi-

nation current

at

the

inception

of

the tail. Since the base

current

of

the

p-n-p bipolar

transistor

corresponds

to

the

MOSFET

drain

current,

the

current

gain

of

the

p-n-p

transistor

is

then,

given by

[1]:

/3 Q1

IMOS

This

current

gain,

BF

parameter

in

SPICE,

allows

to

adjust

the

abrupt

fall

amplitude

and

implicitly

the

fall time

value,

this can be

also

adjusted

directly

by

the ideal forward transit time

of

the

parasitic

n-

p-

n

transistor

 parameter

TF in

SPICE).